Giardia surface antigens undergo antigenic variation. To determine the relatedness of one variant to another, cDNA libraries of two related variants were successfully produced and screened with surface specific Mab or previously defined DNA probes. Analysis and sequencing are in progress. Pulse field gradient analysis of Giardia chromosomes continue. One minor band was related to one of the major chromosomes. Markers were derived product is recognized by all infected animals and humans. Sequencing of this gene revealed no relationship to other proteins. This antigen may be valuable for detecting Giardia specific antibody responses. Attempts to transform Giardia continue. Constructs were made using a Giardia heat shock promoter and he lacZ gene and used to transform Giardia. Giardia were transformed transiently.